Why do we use Direct Online Starter(DOL) || Dol starter

Summary

The DOL Starter, or Direct On Line Starter, is a straightforward method for starting a 3-phase induction motor by directly connecting it to the supply line. It features a simple control circuit with a green start button and a red stop button, along with a Motor Circuit Breaker (MCCB), contactor, and overload relay for protection. Despite the high inrush current, which can be 5-8 times the full load current, the DOL Starter is suitable for small motors, particularly 3-phase squirrel cage induction motors, where the inrush current does not cause significant voltage drop.

Takeaways

• 🔌 A DOL Starter, or Direct On Line Starter, is used for starting a 3-phase induction motor by connecting it directly to the power supply.
• ⚙️ The starter applies full line voltage to the motor terminals without causing harm, thanks to its protective devices.
• 🛠️ It includes a motor overload relay shown in the wiring diagram, which is essential for the starter's operation.
• 💡 The wiring diagram consists of a simple Hold ON contactor circuit with an overload relay for basic motor control.
• 🔘 The DOL starter has two buttons: a GREEN button to start the motor and a RED button to stop it.
• 🔐 It incorporates an MCCB (Motor Circuit Circuit Breaker) or circuit breaker, a contactor, and an overload relay for motor protection.
• ⚠️ The overload relay is crucial as it detects if the motor's current exceeds the rated amperage, preventing damage to the motor winding.
• 🔁 When the green push button is pressed, the motor starts, drawing a high inrush current, which decreases as it reaches rated speed.
• ⚡️ Direct on line starters are suitable for use when the high inrush current won't cause an excessive voltage drop in the supply circuit.
• ⭐ Direct on line starters are commonly used for small motors, particularly 3-phase squirrel cage induction motors.

Q & A

What is a DOL Starter?

A DOL Starter, also known as a direct on line starter, is a method used to start a three-phase induction motor by connecting it directly across its three-phase supply and applying the full line voltage to the motor terminals.

How does a DOL Starter protect the motor?

A DOL Starter protects the motor through the inclusion of protection devices such as motor overload relays, which are designed to detect and prevent potential damage from excessive current draw.

What is the purpose of the green and red buttons in a DOL Starter?

The green button is used to start the motor, while the red button is used to stop it. These buttons control the contacts within the starter circuit.

What components are typically included in a DOL Starter?

A DOL Starter typically includes an MCCB (Motor Circuit Circuit Breaker) or circuit breaker, a contactor, and an overload relay for protection.

Why is an overload relay important in a DOL Starter?

An overload relay is crucial in a DOL Starter because it monitors the motor's current. If the current exceeds the rated limit, the relay opens, causing the contactor to turn off and thereby preventing damage to the motor windings.

What is the significance of the high inrush current in a DOL Starter?

The high inrush current in a DOL Starter can be up to 5-8 times higher than the full load current. This current helps the motor to start but decreases as the motor reaches its rated speed.

In what circumstances should a DOL Starter not be used?

A DOL Starter should not be used when the high inrush current of the motor would cause an excessive voltage drop in the supply circuit, as this can affect the performance of other equipment on the same circuit.

What alternative starter is recommended to avoid high voltage drops?

To avoid high voltage drops, a star-delta starter is recommended instead of a DOL Starter, as it provides a more controlled starting sequence for the motor.

For what types of motors are direct on line starters commonly used?

Direct on line starters are commonly used for starting small motors, particularly three-phase squirrel cage induction motors.

How does the wiring diagram of a DOL Starter typically look?

The wiring diagram of a DOL Starter typically includes a simple hold-on contactor circuit with an overload relay, as shown in the script, which illustrates the connections for starting and stopping the motor.

What is the role of the thermal overload contact in a DOL Starter?

The thermal overload contact in a DOL Starter is a normally closed contact that opens when the motor current exceeds the overcurrent limit, thereby protecting the motor from potential damage due to overheating.